Can P0420 cause no power, rough idle, improper shifts, or limp mode?
What is your question?
I have a P0 420 code and I've replaced the catalytic converter and o2 senser once, cleared the code then months later had the same code again so I gutted the converter but no change. Other repairs incude head gasket replacement, 2 transmissions, timing chain, tensioner, spark plugs... Also replaced the TCM and Nissan said it did not need reprogramming. It will not go over 40 mph or make it up an incline without slowing to a crawl, will not shift past 3rd gear or shift at the proper times and has rough idle when put in gear. I was under the impression that it's in Limp Mode to prevent any further damage but obviously I'm overlooking something. Also while watching the live data on my scan tool, the Load % reads 0% at idle, revs or highway speed. Should be reading around 15% or so at idle and around 95% when revving it. Don't quote me on the numbers, I am a technician (not for Nissan lol) but always learning. Please help me guys and gals. My buddy has been driving me insane over this.
What makes this problem better or worse?
Nothing at all.
How long has your 2005 Nissan Altima had this problem?
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Hello, P0420 itself indicates catalyst inefficiency has been identified. This is likely caused by an ineffective catalytic converter being utilized. You may have replaced one that was spent with one that isn't up to the task of burning the contaminants and exhaust gases effectively enough. This would cause the code to return. Then you mention "gutted the converter" and I'm not sure what that means. Doesn't sound positive though.
Sounds like you've made a tremendous effort to repair multiple areas of the vehicle. And it seems like much of it is educated guesses and consulting someone at your local Nissan dealership -- which isn't really going to be as effective as being a factory trained technician using proper diagnostic equipment and referring to workshop manuals and wiring diagrams.
It is too much, too convoluted and has had too much done already to make any valid suggestion here. So I'll advise to seek guidance at a local shop near you, where all work performed to date can be evaluated hands on and advice can be given moving forward in the best way.
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